In anaesthetic treatment of patients that are connected to a respirator, anaesthetic is added to the inhalation medium that may be air or oxygen. In the following, for the sake of simplicity the term air is used, but applies also with regard to oxygen. Upon exhalation, a part of the anaesthetic trails the exhalation air. Traditionally, this exhaled anaesthetic was lost.
In order to improve the economy in anaesthetic treatment, it has been known for a long time to take actions for recovering exhaled anaesthetic. This is based on the provision of an anaesthetic absorber in the breathing pipe having the function of being able to absorb anaesthetic upon exhalation and to desorb the absorbed anaesthetic upon inhalation. Accordingly, the anaesthetic that is supplied to the patient upon inhalation is composed of continuously supplied new anaesthetic as well as of anaesthetic recovered by the device. Such a device is disclosed in, among others, U.S. Pat. No. 5,044,362.
A disadvantage of such a device is that when the anaesthetic treatment is to be terminated and consequently supply of new anaesthetic to the breathing pipe is turned off, still a certain supply of anaesthetic will proceed. This is because, upon each inhalation, the absorbed anaesthetic is released and supplied to the patient. However, the amount of anaesthetic that subsequently being exhaled and absorbed again decreases for each breath, since a part is absorbed by the patient. Therefore, the supply of anaesthetic will decay gradually. This takes place during a space of time of some minutes.
The consequence becomes that the point of time for awakening after the anaesthetic treatment becomes diffuse, and the patient will be anaesthetized a couple of minutes in excess of what is required. As an alternative, the (nurse) anaesthetist may turn off the supply of anaesthetic a couple of minutes in advance. However, this implies increased demands on the (nurse) anaesthetist and creates the risk of faulty manipulation and faulty timing as regards the turn off.
By EP 855924, a device is previously known that partly takes this problem into account. Hence, in the device disclosed therein, the absorption body is rotatable in the housing so that it either is turned in a way so that the absorption body is active or in a way so that the breathing gas passes around the absorption body. In the latter position, the absorption body is mainly passive and absorbs only very little anaesthetic. However, the known device has certain disadvantages such as that the absorption body may run the risk of ending up in intermediate positions, that it may become damaged while turning. Moreover, the flow duct becomes narrow in the passive position. Finally, the construction presumes a relatively extended absorption body, which causes high flow resistance in the active position.
Therefore, the object of the present invention is to provide a device for the supply of anaesthetic to a patient enabling a complete cut off of the supply of anaesthetic to the patient when the supply of new anaesthetic is cut off, without being impaired by the disadvantages that are inherent in previously known devices of similar type.